avoids jQuery's event system when binding on observes which fixes #280

[justinbmeyer]

This avoids jQuery's slowish event system for observes. It also adds can.listenTo and can.stopListening which work similar to backbone's methods of the same name.

[imjoshdean]

I'd love to have another one of your 15-30 minute lunch sessions where you explain the performance gains we get from this.

[justinbmeyer]

A session isn't likely necessary for this one.

jQuery does a lot of special things when registering an event listener: https://github.com/bitovi/canjs/blob/master/lib/jquery.1.9.1.js#L2721

For example, it handles special events, event delegation, namespaces, events on HTMLElements.

Our addEvent does far less:

https://github.com/bitovi/canjs/blob/master/util/event.js#L8

It basically pushes the handler on an array.

There's a LOT of event binding going on when you render 200 items in TodoMVC. It was the dominate part of the runtime. We replaced the observable event binding with something MUCH faster.